Computers are just like us, they're really bad at getting rid of stuff they don't need any more. All this junk builds up and makes it hard for them to find the information they need, so they slow down. Cleaning it up will give your computer a new lease of life.
Be careful, though, there are lots of programs and apps that claim to do this but which can really mess things up
Sometimes, your computer won't start properly, or you can't get to your pictures or documents. Often, this is because your hard drive has stopped working properly. This can be stressful, especially if you haven't got a backup. However, I find that 9 times out of 10 the data is easily recoverable.
Note that this is a job that requires me to take the computer away and take the drive out. Usually, that isn't a major problem, and the job can be done in an hour of my time on most desktop and laptops. However, some devices are awkward to open, so will take longer. I'll give you an estimate before starting work.
If your hard drive has failed, you'll either need to replace it or the whole computer. I'm happy to advise on appropriate solutions, but I don't sell hardware myself.
When you bought your computer, it was fitted with a certain amount of RAM, which was probably plenty at the time. Over the years, though, programs have got bigger and more memory-hungry. RAM is the memory that they need to use, so often fitting an upgrade will make your machine much more comfortable to use.
As with hard drives, this is a job for which I need to take the computer away. The same caveats apply; I'll assess the job before I proceed and give you a price.